Linerless labels are becoming increasingly more popular due to the inherent advantages associated therewith, as a result of not requiring a separate release sheet. Typical linerless labels are disclosed in U.S. Pat. Nos. 5,292,713 and 4,978,415, and co-pending application Ser. Nos. 07/912,851 filed Jul. 13, 1992 (263-779), 07/907,511 filed Jul. 1, 1992 (263-811), 07/982,699 filed Nov. 30, 1992 (263-929), 08/078,918 filed Jun. 2, 1993 (263-1036), and 08/517,634 filed Aug. 22, 1995 (263-1376), the disclosures of which are hereby incorporated by reference herein.
The release layer is an important aspect of the linerless labels. Previous release layers have generally been too tight and inconsistent, resulting in a non-continuous release. In addition, the previous release layer""s characteristics tend to deteriorate over time. Also, the previous release layers suffered from yellowing, thus detrimentally affecting the appearance of the linerless label. Still further, previous release layers were formed of a hard silicone, which tends to come off during printing and with age.
According to the present invention, a release coating for linerless labels is provided. The release coating includes about 60-80%, preferably about 70%, by weight of a first silicone; and about 20-40%, preferably about 30% by weight of a second silicone. The first silicone may have a specific gravity at 25xc2x0 C. of about 1.0 g/cm3, and the second silicone may have a specific gravity at 25xc2x0 C. of 0.97-0.99 g/cm3. In addition, the first silicone may have a flash point  greater than 100xc2x0 C., and the second silicone may have a flash point  greater than 100xc2x0 C. The release coating may further be provided with about 2-5%, preferably about 3% of total silicone weight of a photo initiator.
According to another aspect of the invention, there is provided a release coating for linerless labels that includes about 70%, by weight silicone having the characteristics listed in Table 1, and about, by weight silicone having the characteristics listed in Table 2.
According to yet another aspect of the invention, there is provided a method of making a release coating for linerless labels. The method includes mixing about 60-80%, preferably about 70%, by weight of a first silicone and about 20-40%, preferably about 30%, by weight of a second silicone. The method may further include maintaining a temperature of the mixture at at least about 49xc2x0 C. and/or maintaining a viscosity of the mixture at about 340-450 cps, preferably about 350 cps.
According to still another aspect of the invention, there is provided a method of applying a release coating to a substrate. The method includes mixing about 60-80%, preferably about 70%, by weight of a first silicone and about 20-40%, preferably about 30%, by weight of a second silicone; processing the substrate; picking up the mixture with a roller; depositing the mixture onto the substrate; smoothing the mixture onto the substrate with a smoothing roller; and passing the substrate through a curing system with nitrogen inertion.
According to still another aspect of the invention, the release coating of the invention is suitable for use as a direct thermal label.
According to still another aspect of the invention, there is provided a linerless label including a substrate having a moisture content between 2-6%; and a release coating coated onto the substrate and having about 60-80% by weight of a first silicone and about 20-40% by weight of a second silicone.
It is an object of the present invention to provide a release coating for linerless labels, a method of making the release coating and a method of applying the release coating that overcome the problems noted above in prior release coatings. This and other objects of the invention will become clear from an inspection of the detailed description, when read in conjunction with the accompanying drawings.